Only thing I know of is that people with a router of the brand Thompson who use Telia or Telenor can have alot of problems like high MS or getting stuck in loading screens. There's something you can do to fix it though, forward ports or something, I cannot remember. Call them.

you've been playing with 120-150ms for a few months now? that's pretty bad. do you just not care much about it or can't help the situation?
anyway, routing issues can arise from time to time, they're kind of a bitch to deal with.

first off, you should log on to whatever server you play on, then check your connections.
find the IP that is associated with wow.exe(don't play anymore so don't remember what IP range/ports), one of them will be bnet/chat/etc and the other the actual server. do a traceroute.
check the traceroute and find out at which hop the problem starts. it can be caused by saturated bandwidth or other hardware issues.

whoever it is, try contacting that company, describe the issue and attach traceroute.
e-mail same thing to your ISP as well.
it's usually not directly your provider's fault, since they just rent the lines, it can be difficult to find who's responsible...
they may or may not care, don't hold your breath, but it's certainly worth a try.

easier solution is to change ISP, if you're able to. ask someone with that particular ISP to do a traceroute, make sure everything is ok before you switch.

gl

ps: I had a routing issue to QL for half a year with my previous provider, so... these things can def. last a while if not taken care of.